Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $48.82   10.183%   $53.7913   $53.79   $53.80   $53.80  
  Purchase #2 $116.47   12.369%   $130.8762   $130.88   $130.90   $130.90  
  Purchase #3 $84.72   10.153%   $93.3216   $93.32   $93.30   $93.30  
  Purchase #4 $228.84   13.279%   $259.2277   $259.23   $259.25   $259.20  
  Purchase #5 $234.81   11.594%   $262.0339   $262.03   $262.05   $262.00  
  Purchase #6 $199.82   5.441%   $210.6922   $210.69   $210.70   $210.70  
  Purchase #7 $79.66   8.804%   $86.6733   $86.67   $86.65   $86.70  
  7 purchase totals = $993.14       $1,096.6162   $1,096.61   $1,096.65   $1,096.60